It is actually the junction of several walls made in various times and locations but the majority of it was built during the Ming dynasty.
Today it is one of the most famous tourist attractions in the world. It is considered one of the greatest architectural projects in human history, with the longest duration and cost in human effort.
The Great Wall is made of stone, wood, rammed earth and brick. It has been rebuilt, perfected and repaired over the centuries. The earliest wall sections were made as early as the 7th century under the Qin dynasty, and the rule of Qin Shi Huang, who had conquered all his opponents' kingdoms and founded the first Empire of China.